Replace netstat by ss

ss(8) is a modern replacement for netstat(8). The former is slowly replacing
the latter in major Linux distributions, which makes it necessary to switch
at some point.

This addresses #278.

Signed-off-by: Karol Babioch <kbabioch@suse.de>

docker-bench-security.sh

@@ -19,7 +19,7 @@ myname=$(basename "${this_path}")     ## file name of this script.
 export PATH=/bin:/sbin:/usr/bin:/usr/local/bin:/usr/sbin/
 
 # Check for required program(s)
-req_progs='awk docker grep netstat stat'
+req_progs='awk docker grep ss stat'
 for p in $req_progs; do
   command -v "$p" >/dev/null 2>&1 || { printf "%s command not found.\n" "$p"; exit 1; }
 done